1. Field of the Invention
The present invention relates to the automatic fusion welding of rails.
2. Description of the Related Art
The enclosed arc welding and thermit welding processes are widely employed for the field welding of rails, since they do not require that the rails be pressed together in the direction of the rail axis during welding. However, enclosed arc welding is not in automatic fusion welding process and, therefore, takes a long time, and the quality stability of the welded joint depends on the skill of the welding operater. The thermit welding is quicker when field welding rails. However, discontinuities or weld defects are likely to occur in the thermit-welded joints, the soundness of which also depends on the skill of the welding operator. To overcome these drawbacks, many processes of automatic fusion welding have been studied as an alternative process for welding rails, and a process was disclosed in Japanese Examined Patent Publication (Kokoku) No. 44-24249 as an alternative to enclosed arc welding and thermit welding. In this known process, the rail base is welded by submerged arc welding and the rail web, head and other portions are welded by electroslag welding.
The known process has advantages in that it does not require that the rails be pressed together in the direction of the rail axis, because it is a fusion welding process, and in that an improved efficiency is expected in comparison with the enclosed arc welding. However, several problems still remain, as follows.
In the known process, the slag formed during the submerged arc welding must be removed at the completion of each welding run. Moreover, when welding of the rail base is completed, the welding is interrupted and then the electroslag welding is carried out to weld the rail web and head. This causes a lack of fusion, hot cracks, and other weld defects upon the initiation and the termination of each run of welding, which lead to an impairment of the process efficiency. Further disadvantages arise in that different fluxes, varied welding machine conditions, etc., are required for welding the rail base and for welding the rail web and head, and these operational complexities will result in a lowered efficiency, the need for expensive welding equipment, and a complex management of consumable materials.